The aim of this proposal is to investigate the events that are involved in genetic recombination in the yeast, Saccharomyces cerevisiae. We propose to examine this question by investigating a genetic region that undergoes high frequency meiotic gene conversion. Three genes near the end of chromosome I are physically mapped within 9 kilobases of each other. The genetic distance in this region is almost 15 cM in length - more than three times the expected genetic distance. An allele of one of the genes, exhibits 20% gene conversion. The unusually high levels of recombination shown by this region will be studied genetically by introducing closely spaced heterozygous sites within the region. The heterozygous sites will act as monitors for both reciprocal and non-reciprocal recombination events within the region during meiosis. After systematically replacing DNA segments within this region by gene substitution techniques, we will assess the effect of the substitutions by measuring recombination in the altered region. It is hoped that the molecular basis of polarity and parity, two properties of gene conversion, will be revealed by this analysis. We plan to investigate how different regulatory states of a region affect homologous recombination. We plan to investigate initiation of genetic recombination in mutant cells that fail to undergo gene conversion. Finally, we will investigate recombination near the free ends of DNA molecules that are modified in vitro, by measuring the segregation of three linked genetic markers after DNA transformation. It is hoped that understanding the precise nature of genetic recombination in a simple eukaryote will serve as a paradigm for genetic recombination in higher cells.